The G-Lader is a scroll-type supercharger used in various Volkswagen models. Its purpose is to increase the horsepower attainable with a given engine displacement. Since it is not enough simply to inject more fuel, as this produces too rich a fuel/air mixture, more intake air has to be added at the same time. This can be achieved with an exhaust-driven turbocharger or a belt-driven compressor. The G-Lader is in the compressor category, since it is belt-driven and does not have the turbocharger problem known as "turbo lag."
This type of air pump, notable for low noise and high efficiency, was patented on October 3,1905 by Léon Creux of France (French Patent 801.182, US Patent 801182). Due to the very imprecise production methods of the period, however, it was not manufacturable for a long time, since the displacer inside the compressor comes within tenths of a millimeter of the housing wall without making contact. Only with the more advanced engineering methods of the 1980s did it become possible to produce the G-Lader. Contrary to expectations, Volkswagen's often problematic designs turned out to need relatively frequent repair in normal operation, which was one of the reasons why that manufacturer eventually abandoned this technology. The main cause of its relatively high repair rate was that Volkswagen misrepresented the G-Lader as maintenance-free. Depending on RPM, load, and design details, various parts wear out, with results ranging from impaired performance to the destruction of the G-Lader. Yet it is frequently possible to extend the life of the G-Lader, sometimes to several hundred thousand kilometers, by periodically rebuilding it with suitable replacement parts.
Driven by the eccentric shaft, which is connected to the displacer shaft by a small belt, the displacer moves eccentrically with respect to the supercharger housing (like the rotor in a Wankel engine) and, through this motion, forces the intake air into a shrinking space, ultimately producing a maximum air overpressure of 0.8 bar(g).
The German name G-Lader comes from the shape of the supercharger (Lader), which looks like the letter G. The displacer's spirals have a width of either 40 mm or, in the larger version, 60 mm -- thus the designations G40 and G60 in the names of VW models in which it is used: